Internal combustion engines combust a fuel and air mixture within cylinders driving pistons to produce drive torque. The engine drives a transmission through a coupling device. Air is drawn into the engine and is metered through a throttle. The engine is operated based on a desired air-to-fuel (A/F) ratio. In some instances, the A/F ratio is lean (i.e., reduced fuel) and in other instances, the A/F ratio is rich (i.e., increased fuel). An ignition system initiates combustion of the A/F mixture within cylinders. During vehicle operation, periods of engine idle occur. Engine idle occurs when there is low engine load and there is little or no operator throttle input (i.e., operator not rewing the engine).
Traditional engine control systems include a throttle closed flag that indicates when the throttle is in a closed position. During periods where cruise control is used (e.g., adaptive or standard), interactions between the throttle closed flag and the cruise control can cause drivability and business issues. More specifically, under light engine loads when the throttle closed flag is not true (i.e., the throttle is not considered close), idle speed control operates in a throttle follower mode. In the throttle follower mode spark advance is used, which results in higher engine torque output. If the throttle closed flag goes true (i.e., throttle in closed position), idle speed control transitions to a coast down mode, which retards spark to provide an engine torque reserve and to reduce engine emissions.
Whenever cruise control is implemented and there is a light throttle input, the engine torque output can rapidly change as a result of the throttle closed flag transitioning to true. Thus, the engine control system opens the throttle to compensate and to regain the commanded torque value, resulting in repeated transitioning. This transitioning creates a sense of business and engine RPM oscillation.